Abrasion and corrosion resistant white cast iron



Dec. 8, 1953 A. P. GAGNEBIN ETAL 2,

ABRASION AND CORROSION RESISTANT WHITE CAST IRON Filed Aug. 20, 1951 .ig. a.

ALBERT PAUL GAGNEBIN LESLIE Louas SEIGLE INVENTORS G. ATTORNEY Patented Dec. 8, 1953 ABRASION *AND' CORROSION RESISTANT WHITE .CAST IRON Albert Paul Gagnebim Red Bank, N. J and Leslie Louis 'Seigle, Dorchester, Mass, assignors to The lnternational Nickel Gompany, Inc-. New

York, N. Y.,.acorporation-ofDelaware Application August 20, 1951,-Serial No. 242,722

8 Claims. (01. 75-428) The present invention" relates' to nickelchromium ralloy white cast irons and more particularly "to nickel-chromium alloy white cast irons having a "very fine grain structure and possessing an improved combination of strength, wear ,or abrasion resistance and corrosion resistance.

.I-Ieretofore,'the'art has .endeavored to employ alloy white cast irons in applications where wear or abrasion resistance were required of these materials. However, it has been found'that prior art alloy' white 'cast .irons frequently lacked a satisfactory combination of strength, toughness, corrosion resistance and wear resistance, par.- ticularly in applications such as oil well pump parts. "Furthermore, in applications requiring toughness and corrosion resistance, the prior art has been accustomed to employ'austenitic nickel,

nickel-chromium or nickel-copper-chromium gray cast irons. It'has beenfoundtha't suchrnacast iron employed linithe foregoing .andanalogous applications by the prior art is .the'highchromium, white cast iron containing, .for example, 25% chromium. Although such materials are satisfactory in many'applications, they dov not resist-corrosive attack by strong caustics and suffer the serious disadvantage that they cannotjoe melted in the cupola'furnace, whichis a furnace commonly employedin cast iron foundries .and one: which is the foundrymans most economical-melting tool. Thus, a demandhas existedrin theart' for a cast'iron which would offera satisfactory combination. of wear resistance, score rosion resistance and, strengthtogether withfthe tory-combination of wear or abrasion'resistance," strength, fine-grained structure and corrosion resistance, none, as far as' weareaaware, was entirely successful when carried intopractice roommercially on an industrial scale.

It has now been discovered that a nickekchromium-silicon alloy whiteicastiiron. provides an improved and useful combination of fine grain structure, wear resistance, corrosion resistance; hardness, strengthand toughness when the alloy compositions are maintained within certain critical limits and within a critical rela tionship as defined hereinafter, and that thisiron can be melted readily in a cupola.

It is an object of the'presentinvention-to pro-- vide a new alloy white cast'iron having a very fine-grain structure even in heavy sand cast sections.

Another object of the invention is to-provide a new alloy white cast iron'having a microstructure wherein the carbide phase occurs as the dis.-

' persed phase. I I

The invention also contemplates'provi'ding a new alloy white cast ironhaving :an improved combination of wear or abrasion resistance, strength,- hardness and corrosion resistance as compared'topriorart alloy white cast irons.

It is a further object of'the inventionto provide anew alloywhite'castiron having very high chilling propensity and which can readily be melted in the cupola.

The invention further contemplates providing anew white cast iron roll for rolling-soft metals,"

such :as aluminum, etc., which will provide a bright finish thereon and which will not water mark the soft metals.

.Other objects and advantages will become ap- I parent from the following'description taken in conjunction with the accompanying drawings'in which:

Figure'l is -..a-reproduction of a photomicro- .g-raphtaken at'25 diameters of a priorart alloy white cast iron;

Fig; 2.depicts a reproduction of'a photomicro- I graphtaken at :25 diameters of'an alloy within the-scope of the; invention;

'Fig. 3 shows a reproduction of a photomicro- 3 graph taken-at BOOdia-meters of an alloy within the scope of the present invention; and

templates an alloy white cast iron containing about 3% to about'3.'7% carbon, about 0.5% to about 3% silicon,'about 4% to about 8% nickel, :about 4%toabout 15% chromium, about 0.2% 1

to about 1.5% manganese and the balance essentially iron including small amounts of impurities,

e. g.;5phosphorus and sulfur in' the'amountsusually'found in cast iron,-i. e., inamounts notov-er about 0.4% .and about 0.15%, respectively; Not

more than about 0.2% carbon is present in the uncombined form. It has been found that in order to obtain the improved combination of fine-grain structure, strength, hardness, abrasion resistance, corrosion resistance, wear resistance, high chilling propensity, etc., which characterize alloys within the scope of the invention, the carbon, nickel, chromium and silicon contents must be controlled according to the following relation:

% Chromium 24:

The microstructure of alloys made according to the invention is comprised of a carbide phase and an austenite-martensite phase. The ratio of austenite to martensite in the austenite-martensite phase varies according to the section size, the silicon content, etc., as will be readily appreciated by those skilled in the art.

Alloys of the invention are characterized by a very fine-grain structure even in heavy sections, by high dispersal of the microstructural constituents and by freedom from gross dendritic constituents. It is believed that the fine-grain structure contributes importantly to the unusual combination of properties possessed by the alloy, and this fine-grain structure, together with the high strength of the alloy, enables the use of the alloy in applications where a coarse structure is undesirable, e. g., rolling mill rolls for soft metals, etc. Among the unusual and high properties possessed by the alloy are high strength, toughness, a high combination of corrosion and wear resistance, resistance to thermal shock, uniform and high hardness even in heavy sand cast sections, high chilling propensity, etc.

This unusual combination of properties is obtained when the compositions are controlled within the foregoing ranges, particularly when the carbon content is controlled according to the relationship set forth herein-before. The carbon content should be within the range of about 3% to about 3.7% to provide a critical amount'of carbide dispersed in an austenite-martensite matrix. The hardness decreases at lower carbon contents and undesirable carbide needles occur at high carbon contents. The silicon content is controlled within the range of about 0.5% to about 3% to prevent excessive austenite formation which occurs when the silicon is below about 0.5% and to prevent formation of pearlite and a weakening effect which occurs above about 3% silicon. Silicon has an important effect upon the properties obtained in alloys of the invention and can be used to control the proportion of austenite to martensite in the austenite-martensite phase, inasmuch as increases in the silicon content increase the proportion of martensite. When the nickel is below 4% undesirable pearlite formation occurs and when the nickel is above about 8% excessive austenite is retained. Similarly, when the chromium is below 4% the desired fine distribution of carbide is not obtained and when chromium exceeds about a detrimental effect is encountered which is believed to be associated with ferrite formation. Control of the manganese content is important inasmuch as below about 0.2% inadequate control of sulfur distribution is obtained and above about 1.5% .an excessive amount of austenite is formed.

As pointed out hereinbefore, a feature characterizing alloys of the invention is the exceptionally fine-grain structure found therein. This +w=42 to 5.0

feature is illustrated by the attached Figs. 1 and 2 of the drawing. Fig. 1 is a reproduction of a photomicrograph depicting the microstructure at 25 diameters of an alloy White cast iron containing about 1.5% chromium and about 4.5% nickel (such as is sold under the trade-mark Ni-Hard). The light-colored phase appearing in the microstructure of the aforesaid alloy is a massive carbide phase. Fig, 2 is a reproduction of a photomicrograp-h depicting the microstructure, at the same magnification as Fig. 1, of an alloy of the invention. As illustrated by Fig.

2, the carbides in alloys of the invention appear as a fine, Well-dispersed phase contrasting sharply to the massive appearance of the carbides of Fig. 1. Figs. 1 and 2 represent the structures of the aforesaid alloys at the center of 3 inch sand cast sections, and the specimens from which the aforesaid figures were obtained were etched to darken the austenite-martensite phase but not the carbide phase.

Within the range of alloy compositions contemplated by the invention, and set forth hereinbefore, a special (and preferred) alloy having other advantages is obtained. This special alloy contains at least about 6.8% and up to about 10% or even about 15 chromium, with carbon, nickel, silicon, manganese, etc., within the ranges set forth hereinbefore and with the carbon, nickel, chromium and silicon contents controlled in ac cordance with the relationship set forth hereinbefore. The aforesaid special alloy incorporates the unexpected and unusual discovery that when the chromium content of the alloy is within the aforesaid range, a microstructure which is the complete reverse of the microstructure normally encountered in white cast irons is obtained. Thus, normal alloy white cast irons are characterized by a microstructure wherein the continuous phase is a massive carbide phase and the remainder of the structure is a discontinuous phase usually comprising martensite and austenite. In the aforesaid special alloy of the invention, however, a martensite-austenite phase is the continuous phase and the primary carbides are dispersed therethrough in a discontinuous manner. This unusual reversal in microstructural constituents is clearly illustrated by Figs. 3 and 4 of the drawing. Fig. 3 is a reproduction of a photomicrograph at 500 diameters depicting the structure at the center of a 3% inch sand cast section of an alloy within the invention and containing about 6% nickel and about 6% chromium. Fig. 4 is a reproduction of a photomicrograph depicting the microstructure, at the same magnification as Fig. 3, found at the center of a similar casting made from a preferred alloy within the invention and containing about 6% nickel and about 8% chromium. It will be noted that the carbides found in Fig. 4 are dispersed discontinuously in a continuous austenite-martensite matrix, and that there is marked refinement of the structure as compared to Fig. 3.

In the special compositions wherein the reversal in matrix constituents'occurs when the chromium equals or exceeds about 6.8%, a nickel content of at least about 4% is required as otherwise the aforesaid reversal in microstructural constituents does not occur even with chromium contents of about 6.8% or more. The nickel content of the special composition should not exceed about 8%, as otherwise excessive amounts of austentite are formed and the alloy becomes relatively sof In addition to the amounts of carbon, nickel,

not more "than. a total. of about 3 ofthese elea mentsashould be present These elements maybe considered? as replacing partof the-irncontent offtheaalloy; andlwhen', in" defining thecomposi tiorr. of theialloy; it is stated that' the balancevi's: essentially iron, or=the=balanceis iron, itis not" intended to exclude the'aforesaid impurities-and metalli'ctelements', since the alloys 1 of the inven' tion; areiessentiallythe samezini properties regardlessiofz the presence orabsence'of'the' foregoing impurities and met'allicelements inthe amounts v set forth hereinbefore.

Ailoys? having the aforesaid unusual combination: of: propertiesan'd: made according to the" inventionare characterized by a very fine grain'--- sizezand' aauniform: high hardness even in heavy" sand CaSt l sections.v In addition, chill castings made? of the alloy: have a very fine-grain structure as: compared to' other chillcast alloy white irons;..high1chilling propensity, high-strength and toughness: I

In order to give those skilled in theart'a-better' appreciation of the advantages of: the invention, illustrative compositions'and sand cast-properties of certain white iron castings are set forth in TablesI'and'II; respectively.

TabZe:I.--Composition1 1 Balanreeiron.

Table "Hr-Sand castpro'perties" 1 Obtained on 1.2-inch diameter arbitration her overl2 inch' centers.

'From" the data in TablesI and mu; may be.

a hardness of 555 Brinelln It may he noted? fr0m=Tah1es IandII that alloys No: 4 andZNo.- special alloys--w ithin-- the scope: of the inventiom having the': reversed: structure discussed herein before; it er, a microstructure wherein thecar bides are dispersed discentinuously in an' austen seenthat; alloyjNo. 1, an. alloy. outside. the scope: 1 of the present-invention, hadthe low sandcast;

hardness of only 375 Brinell, whereas alloy No. 2 having essentially thecsame base-composition as alloy No. 1', but having a: carbon-nickel-chromium-siliconlrelationship as, required; by; the. im vention andlas setlforthhereinbeforeghad:asandi casthardnessof anentireldifferentandahighen' IT I;

itef-martensite matrix; pc's sess -aniimproved com'--' bin'ation of pr0perties==as=- compared te allbys N'o'si 2-: and 3 which represent less preferred allb'ys tration ofthe high hard'n'ess" providedin heavy.

sections sand cast' in the alloy provided hy the present 'invention, a' st'ep bar casting i'rr all'oy Noz 2 exhibited a hardness of 550 Brinell in the inch section; 578- Brinell the 1-inch section and 59'0J5iiii1ell both the 2-inch and 4 inch sections.

A's= indicated"hereii'ibefhre, chill"-v castingsof the alloysof the invention also possess" improved? properties. arhitrationhar chillcast'in allby No. 1 (whichi.

as pointed out' hereinbefore; is outside the pres ent invention) had a? hardness 017418 Briiielll whereas a similar arbitration harchillcast in al1by- No.- 2 (which iswithin the present inven=- tion) had" a hardness of" 56 i Brinell'i This' si'genificant'increase in hardness found in alloy No:- 2-as-- compared to alloy No; I" was accompanied by increases-in transverse strength and in toughness. chill hlbck'sof alloys Nos: 2 and 3 measur=- ing 6" x" 6' x 2" cast against? a chiller on'- one ofthe" 6"x 2" faces werecompletely whitea'n'd had hard'nesses" at' the chill' face of 725 to- 744' Brihell and 719* to '744 B'rihell; respectively-z These chillcastings had a very=fine-gra-instruck ture:

As'illustra-ted hy comparing'Fig; 4 Wil71iFig 3*, the microstructure 'of special? alloys 'ofthe' inverttion' is unexp'ectedly'fine even as compared-"to--- other'alloys withinthe invention but containing less than' the preferred amount of at least" 618% chromium; This' discoveryr is believed due to the dispersal of the carbide phasea con-- tinuous austenite-martensite matrix which has been found to *occur: in special" alloys of the": in-

vention. Those skilled in the art will 'appreciat'e that 'the continuous austenite-martensitematrix of-th'e pref erred alloy provides" a tougher product; having-1 improved resistanceto thermal and me-"= chani'caP shock; ascompared to less preferredalloys' of'the invention having a continuouscar-'- bide network structure:

Preferred alloys made according to the inve'mtion have improved strength and toughnesswhen compared to the= commonly used white cast ironscontaining about chromium and 45.1% nickel (such as" are sold under" the trade-mark Ni' -Hard For example,- when tested in the form of 1 .2 -i'nch diameter "sand" cast" arhit'ratiorrbars; preferred alloys of the invention-are abnut 30% strongerinthe transverse test'and about 20% tougher" in" the impact test" than the comm'only'used 1.5%1chromium-415% nickel white cast irons. In addition; theall'oys'of'the inven:

tion provide superior properties. in the chillicast condition to. alloys ofth'e commonly usedll.5'%. chromiums lfiyl nickel. white cast. irons. The; improved .sand .castdstreng thlfound .in. preferred.

'alloysrofl the invention,- as. compared to .prior: art/ alloywhite cast-irons, provides 2 the :great: practiw cal advantage; over. such. materials that articles having amintricate shape; etcE w-hich arezdiffieculttto. cast in azchillmoldmay now'be .cast satis-rs For example; a 1.2-inch diameteri factorilyyin sand molds when the alloy of the invention is employed.

. Corrosion tests conducted in aerated dilute sulfuric acid and in aerated simulated mine water (0.8% ferric sulfate) show that the new materials have superior corrosion resistance as compared to the commonly used 1.5% chromium- 4.5% nickel white cast irons. For example, sand cast corrosion test specimens in the commonly used 1.5% chromium-4.5% nickel white cast irons corroded about 2.2 times faster than sand cast specimens of the new material when tested in aerated dilute sulfuric acid and about faster when tested in aerated simulated mine water.

-Field tests in handling abrasive materials, suchas blasting shot, etc., have shown that alloys within the invention have excellent resistance to abrasion or wear and are comparable in this respect to the commonly used 1.5% chromium-4.5% nickel white cast irons. It is believed that the fine dispersal of carbides found in alloys of the invention contributes importantly'to the good wear resistance thereof.

The present invention is particularly applii cable to castings requiring an improved combination of fine-grained structure, strength, hardness, Wear resistance, and corrosion resistance not provided by alloy white cast irons heretofore commonly used in the art. For example, oil well pump parts used in pumping abrasive and corrosive crudes may advantageously be made from the alloy of the invention, Highly stressed components, such as parts for gyrator crushers, grinding mill roll heads, stamp shoes or crusher teeth also provide another application for the new material. A particularly suitable application for the new alloy and one where the fine grain thereof is particularly useful is in rolls used for rolling soft metals, such as aluminum, etc., wherethe watermark produced on such metals by prior art cast iron rolls is minimized or eliminated due to this extremely fine grain. Among the other applications of the new material are the following: grizzly discs, rabble arms, clay angers, dredging equipment, sludge pumps, valve seats, impellers, etc.

The special white cast iron compositions contemplated by the present invention can be melted in the usual foundry melting equipment employed for melting alloy white cast iron, e. g., the direct or indirect arc furnace, the induction furnace, fuel-fired melting furnaces (such as the air furnace), etc. A special feature of the white cast irons provided by the invention is that they may readily be melted in the cupola furnace.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. As a new article of manufacture, a white iron casting having included sections at least about one-half inch in thickness and being char acterized by a fine-grain structure by a microstructure containing a primary massive carbide phase dispersed in a discontinuous manner throughout a continuous martensite-austenite phase and containing about 3% to about 3.7% carbon, about 0.5% to about 3% silicon, about 4% 8 to about 8% nickel, about 6.8% to about 15% chromium, the carbon, silicon, nickel and chromium being present in such amounts a will sat-- isfy the relationship expressed in the equation 3.7% carbon, about 0.5% to about 3% silicon.

about 4% to about 8% nickel, about 6.8% to about 10% chromium, the carbon, silicon, nickel and chromium contents being so related to each other that the sum of the percentage of carbon plus the percentage of nickel divided by 28 plus the percentage of chromium divided by 24 plus the percentage of silicon divided by 4 lies between 4.2 to 5.0 inclusive, about 0.2% to about 1.5% manganese and the balance substantially all iron, said casting being characterized by a very finegrain structure and by a microstructure containing a discontinuous primary carbide phase dispersed through a continuous martensite-austenite phase.

3. A casting having included sections at least about one-half inch in thickness comprised of a martensitic white cast iron containing about 3.0 to about 3.7% carbon, about 0.5% to about 3% silicon, about 4% to about 8%nickel, about 4% to about 15% chromium, the amounts of carbon, silicon, nickel and chromium present in any given alloy being further limited in that their respective amounts must fall within the range allowed by the equation Ni Cr Si about 0.2% to about 1.5% manganese and the balance substantially all iron, said casting being characterized by a Very fine-grain structure.

4. As aflnew article of manufacture, a white cast iron roll characterized by a fine-grained structure and by a microstructure containing a discontinuous massive carbide phase dispersed throughout a continuous martensite-austenite phase andcontaining about 3% to about 3.7% carbon, about 4% to about 8% nicktmm, to about 15% chromium, about 0.2% to about 1.5 manganese, with the balance essentially iron, and with the carbon, silicon, nickel and chronlilium being correlated according to the relations 1p:

5. As a new article of manufacture, a white cast iron roll characterized by a fine-grained structure and by a microstructure containing a a 6. As a new article of manufacture, a white I cast iron roll characterized by a fine-grained structure and containing about 3% to about 9 3.7% carbon, about 4% to about 8% nickel, about 4% to about 15% chromium, about 0.2% to about 1.5% manganese, with the balance essentially iron, and with the carbon, silicon, nickel and chromium being correlated according to the relationship:

% Cr N i Si '7. The method of producing a martensitic alloy white cast iron which comprises establishing a cast iron bath containing about 3 to about 3.7 carbon, about 0.5% to about 3% silicon, about 4% to about 8% nickel, about 4% to about 15% chromium, about 0.2% to about 1.5% manganese and the balance essentially of iron, adjusting the composition of said bath such that the chromium, silicon and nickel contents are correlated with the carbon content of said bath according to the relationship:

and thereafter casting said cast iron bath to obtain a martensitic white cast iron casting having included sections at least about one-half inch in thickness and characterized by a very fine-grain structure.

8. The method of producing a martensitic alloy white cast iron which comprises establishing a cast iron bath containing about 3% to about 3.7 carbon, about 0.5% to about 3% silicon, about 4% to about 8% nickel, about 6.8% to about 15 chromium, about 0.2% to about 1.5% manganese and the balance essentially of iron, adjusting the composition of said bath such that the chromium, silicon and nickel contents are correlated with the carbon content of said bath according to the relationship:

and thereafter casting said cast iron bath to obtain a martensitic white cast iron casting having included sections at least about one-half inch in thickness and characterized by a very fine-grain structure and by a microstructure containing a discontinuous primary carbide phase dispersed throughout a continuous martensite-austenite phase.

ALBERT PAUL GAGNEBIN.

LESLIE LOUIS SEIGLE.

' References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,988,912 Merica Jan. 22, 1935 2,189,131 Cape et a1. Feb. 6, 1940 

1. AS A NEW ARTICLE OF MANUFACTURE, A WHITE IRON CASTING HAVING INCLUDED SECTIONS AT LEAST ABOUT ONE-HALF INCH IN THICKNESS AND BEING CHARACTERIZED BY A FINE-GRAIN STRUCTURE BY A MICROSTRUCTURE CONTAINING A PRIMARY MASSIVE CARBIDE PHASE DISPERSED IN A DISCONTINUOUS MANNER THROUGHOUT A CONTINUOUS MARTENSITE-AUSTENITE PHASE AND CONTAINING ABOUT 3% TO ABOUT 3.7% CARBON, ABOUT 0.5% TO ABOUT 3% SILICON, ABOUT 4% TO ABOUT 8% NICKEL, ABOUT 6.8% TO ABOUT 15% CHROMIUM, THE CARBON, SILICON, NICKEL AND CHROMIUM BEING PRESENT IN SUCH AMOUNTS AS WILL SATISFY THE RELATIONSHIP EXPRESSED IN THE EQUATION 